Trace Element Analysis of Pyrite from the Zhengchong Gold Deposit, Northeast Hunan Province, China: Implications for the Ore-Forming Process

Abstract

The Zhengchong gold deposit is located in the central segment of the Jiangnan Orogen in northeastern Hunan Province, South China. The host rocks of this deposit are the Neoproterozoic slates of the Lengjiaxi Group and granodiorite. The structures in the Zhengchong gold deposit are dominated by NE-trending reverse faults, which control the gold-bearing veins. The orebody consists of NE-trending laminated quartz veins and NW-trending quartz veins. The alteration styles include silicification, carbonatization, sulfidation, sericitization and chloritization. The Zhengchong gold mineralization can be divided into four stages: Quartz-pyrite (stage I), quartz-pyrite-arsenopyrite (stage II), quartz-polysulfide (stage III) and quartz-carbonate (stage IV). Three generations of hydrothermal pyrite were identified: Disseminated euhedral to subhedral cubes in altered wall-rock (PyI), euhedral to subhedral cubes inter-grown with arsenopyrite and tetrahedrite in quartz veins and wall-rock (PyII), and euhedral cubes with microinclusions (native gold, galena, sphalerite, chalcopyrite, tetrahedrite, and pyrrhotite) or metasomatic textures in sulfide-rich veins or veinlets (PyIII). PyII and PyIII are arsenian pyrite and represent the main Au-bearing minerals. PyI records the lowest concentrations of Au; PyII and PyIII record similar amounts of Au, Cu, Pb, Zn, and Bi, but PyIII is more enriched in Co, Ni, Te, and Se. The substitution of As, Se and Te for S and that of Co and Ni for Fe occurs by direct-ion exchange. Invisible gold is uniformly distributed within the arsenian pyrite, and visible gold fills microfractures in PyII or occurs as inclusions in PyIII. Co, Ni, Cu exhibit positive correlations with Au and a negative correlation between Au + Cu + Co + Ni and Fe reflect that Fe vacancies may have been a major cause of the precipitation of invisible Au and other metal elements in pyrite structure. There are systematic trace element differences between the three generations of pyrite (PyI, PyII, PyIII). The more Co, Ni and Se, Te substitution that occurred for Fe and S, respectively, the greater the increase in the Co/Ni ratio (<1) and the decrease in the Se/Te ratio (<10) in stage III, indicating that a more reduced, lower-temperature metamorphic hydrothermal fluid was present in stage III.

Sulfur isotopic and trace‐element compositions of pyrite from the Zankan iron deposit, West Kunlun Orogenic Belt, China: Possible Early Cambrian banded iron formations

“…Numerous studies have used the Co/Ni ratio of pyrite as an indicator to understand the sources and environments of hydrothermal fluids from which this mineral is precipitated (e.g., Bralia, Sabatini, & Troja, 1979; Clark, Grguric, & Schmidt, 2004; Craig et al, 1998; Raymond, 1996). Previous studies have shown that volcanogenic pyrite or pyrite precipitated from magmatic–hydrothermal fluids has elevated Co contents (Cafagna & Jugo, 2016; Shao, Wang, Liu, & Zhang, 2018), whereas sedimentary pyrite, such as that in black shale, has high Ni (rather than Co) contents (Gregory et al, 2015; Large et al, 2009). Consequently, Co/Ni ratios of <1 with low standard deviations are commonly accepted as indicating pyrite of sedimentary origin, whereas pyrite associated with magmatic–hydrothermal fluids has Co/Ni ratios of >>1 (e.g., Bralia et al, 1979; Deol, Deb, Large, & Gilbert, 2012; Koglin, Frimmel, Minter, & Brätz, 2010; Meng, Hu, Huang, Gao, & Sasseville, 2019; Mukherjee et al, 2019; Raymond, 1996; Thomas et al, 2011; Zhang et al, 2014).…”

Ore Genesis and Minor Elements of Orogenic Gold Deposit at Tamilouw– Haya, Seram Island, Indonesia

“…Elements including Se and Te are under detection limit or absent and might indicate that deposit is not associated with low sulfidation epithermal and igneous rocks or intrusionrelated deposit. High concentrate of Se and Te is related to igneous rock, low sulfidation epithermal and Carlintype deposit (Keith et al, 2018;Shao et al, 2018).…”

Genesis of Chaxi Gold Deposit in Southwestern Hunan Province, Jiangnan Orogen (South China): Constraints from Fluid Inclusions, H-O-S-Pb Isotopes, and Pyrite Trace Element Concentrations

“…The Jiangnan Orogen Belt (JOB) is one of the two lode Au-Sb-W metallogenic belts in the world, and over 250 gold-polymetallic occurrences have been reported in it, with a total Au resource of over 970 tonnes (t) [1][2][3][4][5][6]. As a Precambrian terrane extending northeastward for 1500 km, the JOB is a collision zone between the Yangtze and Cathaysia blocks, which formed the South China Block [7][8][9].…”